I tend in that direction. Although the term social Darwinism seems to be used with negative connotations. Evolutionary ethics or evolutionalry psychology are better suited. But people do seem to either not know, ignore or purposely avoid thinking about the evolutionary reasons why we do a lot of what we do.
Evolutionary ethics devolve (forgive the pun) into lifeboat ethics – as you, yourself, have demonstrated a number of times. That is because the assumption of atheism is that human beings are on our own as far as existence and morality is concerned. Where there is no ultimate plan or teleology built into existence itself (which is the fundamental difference between any atheistic moral system and any theistic moral system) then the ground rules can be shifted very quickly.
Take evolutionary ethics which must – at the very least – use survival of some human beings, even at the expense of other human beings as the grounding premise. Anything which threatens the survival of all can be used to rationalize the extinction of many or at least some on the pretext that otherwise the lives of all are at stake.
So, using some kind of doomsday scenario – overpopulation, peak oil, lack of resources, or even global warming – an evolutionary ethicist can argue (quite compellingly it seems to others of the ilk) that there is justification for killing off large numbers of human beings (the old, the unborn, the unproductive, the handicapped) for the sake for preserving at least some human life with a modicum of “well-being” (AKA “the good life.”)
So, “feminists” will argue that they have a “right” to kill the babies in their wombs to protect and secure their own “well-being.” Soon, as the euthanasia ideology works its way through society, governments will use the slippery-slope-is-a-fallacy-fallacy to avail themselves of responsibility for those who cannot contribute to the public good. Wait until the millennials will have to pony up for all their entitlements and find looking after their progenitors is too costly a burden – old bodies (like unborn bodies) will start piling up. Lifeboat ethics (AKA evolutionary ethics) at work. Anything can and will be justified under the rubric of survival of – if not of the fittest – at least of those holding the reins of power to make the rules.
This is the problem with all progressivist thinkers, they can’t or won’t think through the implications of their ideas to complete their thinking. Deep down, they understand where it leads, but have the impression if they don’t verbalize it, no one else will notice or catch on – as if those about to be tossed from the lifeboat are incapable of that depth of thought, but are merely capable of treading water (instead of going deep or walking on it) as far as logic is concerned (again forgive the pun.)
Lifeboat ethics (evolutionary ethics) has to presume there is no higher power in control of everything that happens in order for humans to presume to themselves complete authority to make the rules as far as who gets tossed and who has a “right” to survive. It is a Faustian bargain all around seeing as anyone who accepts the perspective must reduce themselves to a less than human mode of seeing reality.